There are a variety of problems faced by manufacturers who use fluoropolymers for foamed insulation, (e.g. insulated conductor manufacturers), that are not resolved by currently available conductor insulation materials. One such problem for these manufacturers is that the extrusion/melt draw-down process is carried out under a variety of conditions and parameters, resulting in variation of the physical and electrical characteristics of the foamed fluoropolymer for the manufacturers. The manufacturers seek to minimize the variation of the foamed fluoropolymer characteristics.
Another concern of the manufacturers is the economics of extruding the fluoropolymer for a variety of uses. Faced with the onset of insulation quality (spark and/or lump) problems, and at least the uncertainty of changing draw down ratio (DDR), operating temperatures, and cone length, insulated conductor manufacturers typically reduce line speed until the desired quality of the insulated conductor is achieved, which results in a loss of productivity.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,764,538 to Buckmaster et al. discloses synergistic combinations of boron nitride (BN) and certain inorganic salts which provide enhanced foam nucleation in fluoropolymers.
U.S. Pat. No. 4,877,815 to Buckmaster et al. discloses a class of sulfonic and phosphonic acids, and salts of the acids which give very efficient foam cell nucleation in a wide variety of thermoplastic materials at low concentrations. Additionally, these acids and salts are beneficially used in minor amounts in conjunction with boron nitride and calcium tetraborate together, i.e. a combination covered by U.S. Pat. No. 4,764,538. The above-mentioned patents do not disclose compositions that provide the desired insulation crush resistance and electrical performance while extruding at high speeds sought by manufacturers such as insulated conductor manufacturers.
It is desirable to provide a foam structure which reduces variation in the processing and electrical performance of the finished product. It is further desirable to provide a composition that is foamable enabling the reduction of the amount of polymer material required for applications such as cable applications. It is also desirable to have a foamable fluoropolymer composition that can be extruded at higher speeds than presently possible with commercial polymer without risking quality, loss of productivity or desirable characteristics such as the electrical properties of an insulated conductor.